/Engine/Source/Editor/SequencerCore/Public/MVVM/Selection/SequencerCoreSelection.h
Implementers of this class should create a derived type that defines each of its selection sets by calling AddSelectionSet in its constructor. This enables a central implementation for event suppression and broadcast.
class FSequencerCoreSelection : public [TSharedFromThis< FSequencerCoreSelection >](API\Runtime\Core\Templates\TSharedFromThis)
FSimpleMulticas...
OnChanged
Event that is broadcast when any selection state inside this class has changed & after all scoped suppressors have been destroyed